The present invention relates to a multi-voltage electrical system for a vehicle and to a circuit module for isolating a multi-voltage vehicle electrical system.
Vehicles such as passenger cars, trucks, trains and the like occasionally are equipped with a multi-voltage electrical system in which a first subsystem is formed to be operated at a first operating voltage and a second subsystem is formed to be operated at a second operating voltage. In this connection, in particular the 12 V subsystem and the 48 V subsystem for passenger cars are known.
To one of the two subsystems a transceiver can be associated, which via a first ground terminal of the first subsystem, for example in the form of a first ground stud, is connected to ground. The transceiver usually serves for transmitting and receiving control signals, wherein in the transceiver a further processing of the received control signals also can be effected. An example for such transceiver is the LIN (Local Interconnect Network) transceiver. The transceiver can be operated at the first operating voltage, i.e. for example at 12 V.
To the second subsystem a control unit can be associated, such as a microcontroller. The control unit and the transceiver can be integrated in a housing and in so far be mounted as a one-piece component. Via a second ground terminal of the second subsystem, which is arranged spatially separate from the first ground terminal and for example is present in the form of a second ground stud, the control unit is connected to the same ground as the transceiver. Ground usually is the ground of the vehicle.
The control unit generally operates at a voltage of 5 V or 3.3 V. This voltage usually is provided to the control unit via a voltage converter, such as a DC/DC converter or a linear regulator, which correspondingly converts the second operating voltage, for example 48 V. The control unit supplies actuation signals to electronic units of the vehicle electronic system, such as to a driver of a power electronic switch. These electronic units then actuate one or more electric motors of the vehicle, for example an electric vehicle drive, a seat adjustment drive, etc.
The transceiver of the first subsystem is communicatively coupled to the control unit of the second subsystem. For this purpose, a number of control signal paths usually are arranged between the transceiver and the control unit, which connect one or more signal outputs of the transceiver with signal inputs of the control unit and signal outputs of the control unit with the signal inputs of the transceiver. The control signal paths transmit control signals from the control unit to the transceiver and control signals from the transceiver to the control unit. These control signal paths usually are low-ohm direct connections. Such control signal paths are known for example from FIG. 12 of the data sheet AN00093 for the PHILIPS LIN-Transceiver TJA 1020.
In multi-voltage vehicle electrical systems it is problematic that the transceiver of the first subsystem usually is connected to a first ground terminal and the control unit of the second subsystem usually is connected to a second ground terminal spatially separate from the first ground terminal. In the end, however, both the first ground terminal and the second ground terminal are connected with the same ground, namely the vehicle ground, in a star-shaped pattern. When a faulty operating voltage supply occurs in the first subsystem and/or in the second subsystem, compensating currents can occur in the multi-voltage vehicle electrical system and in particular in the control signal paths or within a component connected to both subsystems, which can damage and sometimes even destroy the units of the first subsystem and/or the second subsystem.
In this connection. EP 1 291 998 B1 proposes to provide a galvanic isolation between the two subsystems, i.e. between the two voltage levels, for example in the form of a usual transformer. Furthermore, there are provided monitoring modules which carry out an isolation monitoring of the subsystems. The monitoring modules are integrated in a controller which is connected with at least two voltage levels. The controller furthermore includes a device for separating the connection of one or more subsystems from the controller and/or a device for switching off the controller upon detection of a faulty operating voltage supply.
What is disadvantageous in this known approach is the expensive construction. A plurality of monitoring modules are necessary and, in addition, there is proposed a galvanic isolation by means of a transformer which has a high weight and involves comparatively high costs.
DE 10 2012 215 542 A1 discusses the problem of a common ground connection in a multi-voltage vehicle electrical system. In the case of a disturbance on this common ground line, a polarity reversal of components can occur in the low-voltage subsystem. For the solution of the problem it is proposed to provide a further ground terminal to which measuring means are associated, which are equipped to measure a current flow via the further ground terminal. Furthermore, diagnostic means are provided, which on the basis of the measured current flow diagnose a disturbance in the common ground terminal and/or in the further ground terminal in dependence on at least one operating condition of the multi-voltage vehicle electrical system.